Means for mounting propeller blades



p 1933'- H. ELLINGHAUSEN MEANS FOR MQUNTING PROPELLER BLADES .Filed Nov.21, 1936 2 7n venior 3 iy/mz/zgmsen Patented Sept. 6, 1938 UNITED STATESPATENT OFFICE Hermann" Ellinghausen, Bremen, Germany ApplicationNovember 21, 1936, Serial No. 112,154 In Germany November 23, 1935Claims.

The present invention relates to propellers and more particularly tomeans for fastening the blades of wood propellers to the hub socket.

For some purposes wooden propellers are pre- 5 ferred to themetallicones. The increase of speed resulting from the steadydevelopment of the aeroplanes and which is not yet definitive, onaccount of the large difference of the starting and service speedsalmost generally requires propellers with variable pitch or adjustableblades, and thus a propeller having adjustable wooden blades is ofparamount importance in the construction of aeroplanes.

When however the two blades of a wooden propeller are, separated fromone another with a view to their adjustability the advantage afforded bythe high tensile strength of wood in the direction of its fibres will belost at the hub. On the other hand it has not yet been possible tofasten the wooden blades in the metallic sockets, by

means of which the blades are revolubly connected to the hub in the sameway as metallic blades, in such a manner that this connection is able tosafely and durably stand the centrifugal and vibration forces to whichsuch wooden blades are subjected.

Various systems have already been known which are based on theprospective idea that the centrifugal forces acting in the blade betaken up at as many points as possible; however the manner in whichthese forces are to be taken up by no means corresponds to the magnitudeof the forces developed nor to the conditions of service so that nopractical success was secured in this way.

The present invention relates to means for fastening wooden blades inthe sockets of air propellers and more particularly adjustablepropellers, and the object of the invention is to provide for means bywhich the centrifugal and vibration forces are'taken up in the woodenblades and transmittedgtherefrom to the blade sockets thereof in a verysafe way. This eifect is obtained by the fact that the tensile strengthof the fibres as lost by the separation of the two blades is replaced byone or several areas resisting to shearing forces in the wood of theblades and the size of which corresponds to the stress undergone, andthataccording to the inventionrsuch an arrangement is provided for thata uniform stress in the shearing area or areas is ensured without thetensile and bending strength of the woodenblade being thereby adverselyaffected,

In the accompanying drawing Fig. 1 shows a longitudinal section of ablade, Fig. 2 the blade socket with the stlmip of the blade in a crosssection and Fig. 3 a portion of an anchor in elevation. Referring to thedrawing, the fastening arrangement comprises a plurality of round steel5 rods or anchors a uniformly distributed over the cross section of theblade'stump, secured by nuts 0 in the socket bottom and having adiameter which is towards the free end reduced in a stepby-step manner,these rods having the highest possible tensile strength and carrying aplurality of round steel washers b properly spaced and prevented frombeing stripped off the red by the latter being provided with collarsobtained 15 by upsetting in a red-hot condition. As these collars aremade by upsetting, all fibres of the a steel of the rods remainuninjured and transitions of suilicient radii are formed between thecollar and the rod proper so that in all cross 20 1 sections the saidrods are not injured and may be fully stressed with the particularpermissible stress. As compared with the systems already known thisarrangement not only results in a reduction of weight but also preventsboth the cross section of the blade stump and the glued joints of thewood lamellas from being materially weakened.

The washers I; inserted with the steel rods between at least two layersof the wooden blade will subject an imagined wood cylinder to shear, thediameter of which corresponds to that of the particular washer and thelength of which corresponds to the distance of two adjacent washers.According to loading tests accomplished, the resistance to shear of.sucha cylinder surface is 85 so high that as a rule 7 to 8 washers will besufficient. K

As hereinabove described the rods 0 are attached to the socket by meansof the nuts 0. The socket comprises an outer cup-shaped member 0 havingan annular flange h by means of which the blade may be bolted to thepropeller hub. An inner cup-shaped member I in the nature of a liningmay-be provided within the member e but such an inner member. is notnecessary and forms no part of the present invention.

The steel rods are inserted between the layers of the wooden blade witha definite play so that, when themgts are tightened in order that the 50anchors comprising the rods and washers are put under tension, theserods are allowed to freely move-"in their grooves and to integrallytransmit the stress to the washers. A new effect acting in the samedirection, of the anchors will result and from the rounded shape of thecollars (shown at d) obtained by upsetting. As it is rather difficultpractically to produce the hollow spaces for the washers exactlyregistering in two adjacent layers of the blades, the mobility of thewashers allowing an inclination of them on the anchors will cause auniform distribution of the pressure over the two adjacent layerswithout the rod being stressed unilaterally, the rounded collarspermitting of a corresponding attitude to the washers.

uniformly over all washers of the anchors.

The design and the bedding of these novel anchors thus largely warrantthat tightening the anchors after the blade stump having been introduced into" its socket, by uniformly tightening thenuts, will resultnot only in a uniform initial tension in the various blade and bladestump cross sections but also in an initial tension which is uniformlydistributed over the whole length of each anchor and thus also over acorrespondingly large portion of the wood of the blade. In comparisonwith arrangements already known the novei fastening means furtherdistinguishes itself by the fact that the loose bedding of the washers,developes no forces tending to cleave the glued joints.

I claim:

1. Supporting means for propeller blades formed of wood laminationswhich extend in the direction of the length of each blade comprising, ahub socket for receiving the inner end of the blade, metallic tensionmembers extending into the wood blade and secured to said socket, saidtension .members being uniformly disfrom the loose seating of thewashers on the rods tributed over the cross section of the blade andeach tension member being arranged between two laminations, collarscarried by said tension members and a washer adiacent the hub socketside of each collar for engaging two laminations.

2. Supporting means for propeller blades according to claim 1characterized by the features that the washers are tiltablymounted onthe tension members.

3. Supporting means for propeller blades according to claiml'characterized by the feature that the tension members are embeddedwith play in the adjacentfaces of two laminations of the blade.

4. Supporting means for propeller blades formed of wood laminationswhich extend longitudinally in the direction of the length of each bladecomprising, a hub socket for receiving the inner end of the blade,metallictension members extending into the wood blade, said tensionmembers being uniformly distributed over the cross section of the bladeand each tension member being arranged between two laminations,

means for fastening said tension members to being uniformly distributedover the cross section of the blade and each rod being arranged betweentwo laminations, means for fastening said rods to. said hub socket,arcuate shouldered collars carried by said rods,washers mounted on saidrods adjacent each collar and between the collar and the hub sbcket, andsaid washers engaging two adjacent laminations whereby each washer maytilt on said arcuate shoulders.

. HERMANN EILINGHAUSEN.

